Extensive work has been performed to utilize optical systems for high-end sensor designs. However, unlike digital communications where a signal is interpreted as either a logic high or logic low value, analog sensors must be able to discern a wide range of continuous values. The ability to extend an analog sensor's range of continuous values, as well as increase its resolution within this range, greatly enhances the utility and functionality of such a sensor for high-end applications.
To increase dynamic range and resolution within a dynamic range, feedback control can be used. Feedback control can come from a sensor system illuminated by a light emission source or from a back-reflection of light from a semi-transparent glass cap that is used to seal a discrete light emission system. Both examples can be found in commercially available systems.
While useful, both approaches have several drawbacks and do not fully realize the signal-to-noise ratio (SNR) potential of a light emission system. For example, if a semi-transparent glass cap is mounted directly behind a light source to create back-reflections to a diode, some light may be directly reflected back to the light source. Unfortunately, such feedback directly into the light source can decrease the SNR. This approach can also preclude direct packaging of a light source with the optical sensor system, increasing the size of the optical system. Generally, only light that is reflected at a large enough angle can travel beyond the edge of the light emission source and become collected photo current in a photodiode mounted behind the light source. This unfortunately can reduce the total amount of light available, decreasing the SNR of the respective photodiode. A decrease in SNR makes it more difficult to accurately control and adjust the light source.
There is a need for a system and method for increasing the SNR in optical based detection systems.